rad = rho * cos(radians(sza)) * Es * sc / (pi * d2)
where: d2 = 1.0 / U
scale: 1 / (0.001 * 1000) = 1 (default)

So, I have few questions amongst the two which one is correct. I don’t see any scaling factor in the first one. Moreover, does the incidence angle here denotes the value of Mean_Sun_Angle.ZENITH_ANGLE from file MTD_TL.xml ?

Also, Let’s say i do atmospheric correction using SEN2COR or DOS. I would get the BOA reflectance, right? So, then how do i convert it to a BOA radiance?

If you want to work with atmospherically corrected data, you need to select the appropriate data source (Sentinel-2 L2A). THe parameters SENCOR and DOS are just approximation of this correction and will not make it possible to get results that you are looking for.